Electric motors have a stator and a rotor which is rotatable with respect to the stator. In an outer rotor motor the rotor is disposed around the stator. In a brushless DC motor the rotor has magnetic poles formed or created by one or more permanent magnets, while the stator has windings wound about the stator core to form the magnetic poles of the stator. The stator core is usually formed by a stack of core laminations of silicon steel to provide the magnetic flux path of the stator.
The permanent magnet poles of the rotor are usually formed by arc-shaped or inclined magnets, with even gaps formed between the magnets and teeth of the stator core. The motor with this configuration has a high cogging torque and poor motor efficiency.
In addition, as shown in FIG. 13, a core lamination 100 of a traditional stator core include an annular portion 130, a plurality of teeth 150 extending radially outwardly from the annular portion 130, and a tip 170 disposed at a distal end of each tooth 150. Each tooth 150 is elongated with a large height, i.e. a large distance from a root (where the tooth 150 connects to the annular portion 130) of the tooth to the tip 170. This results in a long magnetic path and hence a high magnetic resistance. The magnetic flux passing through the stator core formed by the core laminations 100 generates a large amount of heat, thus causing a significant iron loss of the motor and hence a poor efficiency of the motor.